1. Field of the Invention
The present invention relates to an actuator to operate a frictional engaing device such as a frictional clutch and a frictional brake, etc., in particular relates to an actuator which converts revolutionary force into thrusting force mechanically.
2. Description of the Prior Art
A power transmission device of a motor vehicle in general such as an automatic transmission or a four wheeel driving device uses a frictional engaging device such as a multiple disc clutch, multiple disc brake (or band), and a differential lock clutch (full-time) or a two or four-wheel switching clutch (part time) to control each component of a planetary gear mechanism.
Previously the frictional engaging device has employed a hydraulic actuator (hydro-thrust conversion mechanism) comprising a piston and a cylinder to press or release the discs.
And as shown in FIG. 2 the mechanism employing the hydraulic actuator works an oil pump by the revolution of an engine, regulates an oil pressure generated by the pump by a hydraulic control mechanism such as a regulator valve, and sends the regulated oil pressure to the hydro-thrust conversion mechanism comprising the actuator through a hydraulic switching mechanism made up by a control valve, etc. at required moment.
By the hydro-thrust conversion mechanism hydraulic pressure is converted into thrust force, the thrust force is applied to the frictional engaging device made up by a multi disc clutch, etc. through a frictional engaging pressing mechanism, and the frictional engaging device is engaged. And this time a sensor detects throttle pressure, vehicle speed and running condition, and sends such signals to a controlling portion (CPU). The electrical signals are sent to each solenoid to control the hydraulic control mechanism and the hydraulic switching mechanism at the required moment.
Furthermore as shown in FIG. 3, as an another example, a solenoid type clutch and brake which converts electric power into thrust force directly without using hydraulic pressure is shown.
Accordingly in the case of hydraulic pressure the problems of oil leakage, response delay, difficulty of precise control and complexity of the mechanism come out, and reliability is sacrificed because the electric signals once are conveted into hydrualic pressure.
In addition if hydro-system is employed an oil pump is required as a source of hydraulic pressure application. The oil pump is directly connected to an engine to work, however the engine itself is not provided exclusively for the oil pump. And the revolution of the engine varies, so, utilizing the engine output to work the oil pump has to have loss and needs extra effort to take out the output of the engine. Another case employs an electric motor to work the oil pump, however this case requires a space for the motor. Consequently such space has to be considered in spite of the space in a vehicle being limited, and efficiency is sacrificed because electric power which is controlable with ease is converted into hydraulic pressure.
On the other hand the mechanism utilizing solenoid power directly has no problems regarding hydraulic pressure mentioned above, however the devices become big and heavy to get transmission power and braking power tantamount to the mechanism utilizing hydraulic power.
The present invention is purposed to provide an actuator for frictional engagement which enables precise and quick control though a size of the device and is comparatively small.